Implantable medical devices that monitor ambulatory patients must have a manner of alerting patients to relevant events. Notification can occur for the detection of medical events such as acute ischemia, arrhythmia, bradycardia, or low levels of insulin. Notification can also be triggered by the detection of low battery levels, device malfunction, signal quality issues, and when device adjustment is merited. In order to provide patient notification the implanted medical device (IMD) can use either internal or external alerting means, or both. In the case of internal alerting, the IMD can use, for example, vibration or sonic alert signals. In the case of external alerting signals, the IMD may communicate with an external device which then produces an alert signal such as a vibrotactile, sonic, or visual signal. Multimodal alert protocols occur when the alert signals are emitted to relay information to multiple sensory modalities.
It is useful to provide both internal and external alerting for medical devices because this increases the likelihood that the patient will pay attention to the alert signal and take appropriate action (e.g., going to the hospital in the case of an emergency alarm related to a dangerous cardiac condition). However, in the daily life of a patient the IMD may not always successfully communicate with the external device. For example, the patient may leave the external device beyond the IMD wireless communication range. Additionally, when the patient is in the shower or swimming an external device is not practical and alert signals may not be noticed by the patient. Further, the external device may not work correctly as may occur if its battery becomes depleted. In these cases it is important that at least internal alerting is available to notify the patient to a serious medical event. Accordingly, it is important to be able to determine that the IMD can successfully provide alerting to the patient.
Vibration alarms have a number of advantages. In the case of both internal and external alarms, patients may prefer relatively silent vibration alarms over sonic alarms that may cause persons nearby to learn about a particular medical condition which is being monitored. In a movie theater visual and auditory alarms may be inadvertently ignored due to saturation of these sensory channels, while there is little interference with respect to noticing a vibration alarm.
Alert transducers may fail in several manners. This is particularly true in the case of a vibration alert which requires moving parts. A transducer may simply fail to operate or may operate in a compromised manner. In the case of vibration, the vibration may be provided at a lower vibration level or frequency than intended. If an electric motor that provides the vibration is not able to product the expected strength, frequency, or pattern associated with the alert signal, then the patient may misinterpret the alert, become unsure as to whether an alert is occurring, or simply not experience it at all. Accordingly it would be an advantage to provide a manner of objectively testing the integrity of alarm signals such as vibration alarms.
Subjective reports of vibration have a number of disadvantages. Older people or diabetics may experience lower levels of vibration due to physiological factors rather than to actual mechanical changes which occur in the motor. If the patient complains that a vibration alarm is not strong enough, a medical professional may pursue different solutions depending upon whether the problem is with the patient or the implanted device. Accordingly would be an advantage to provide a manner of objectively assessing the strength of the alarm signals such as vibration alarms.
Additionally, if a patient fails to respond to an alarm such as when the patient is sleeping, the medical professional may not be able to determine whether the alarm strength was inadequate for the patient and must be increased, or whether the IMD did not actually vibrate as anticipated (or at all!) at the time of the alarm. It would be an advantage to provide a manner of objectively determining if an alarm occurred, and that it occurred as intended, at the time that the actual alarm was triggered. An alarm log of what actually occurred can be valuable both for clinical and legal reasons.
Lastly, when changes in alarm characteristics are small, and alarms occur infrequently (e.g. not more than every 5 months) then a patient may not be able to subjectively assess whether the vibration alarms have changed from how they originally experienced these. Vibrotactile sensitivity for internal vibration signals changes as a function of vibration pattern, frequency and amplitude. It is important to be able to accurately measure any changes which may occur in the IMD's vibration signals so that these can be detected, quantified, and/or compensated for if desired.
The IMD can be any type of implantable medical device. In one embodiment the IMD is a cardiosaver device, as described by Fischell et al in U.S. Pat. Nos. 6,112,116, 6,272,379 and 6,609,023, incorporated herein by reference, which can detect a change in the patient's electrogram that is indicative of a cardiac event, such as acute ischemia and then provide notification. The IMD can also be a medical device which provides drug or electrical stimulation to a neural, vagal-nerve, or other anatomical target. The IMD may be partially implanted, such as an implanted insulin pump/delivery system with an external reservoir. Notification (or alerting/alarming) occurs by way of an internal alarm system within the IMD and/or an external alarm system which may comprise an external, pager-type device, a patient programmer, and a remote station where patient data may be sent for review. The IMD communicates with the external alarm system using wireless communication signal as long as the external alarm system is within range. The external alarm system of the current invention has capabilities equivalent to those described by Fischell et al in U.S. Pat. Nos. 6,112,116, 6,272,379 and 6,609,023. For example, the external alarm system may provide one or more types of visual, sonic and vibratory alerting signals, and may provide voice/data communication between the IMD/patient and a remote medical monitoring station.
The IMD and/or the external alarm system may provide a single type of alarm. Alternatively, at least two types of alarms may be used (“two stage alerting”). In one embodiment a major/critical event alarm (an “EMERGENCY ALARM”) can provide notification of the detection of a serious medical event (e.g., a heart attack which is an AMI) and the need for immediate medical attention, and a less medically significant alert (a “SEE DOCTOR ALERT” or alarm) can signal the detection of a less serious condition that is not life threatening such as exercise induced ischemia or the detection of a depleted battery. The two types of alerting consist of different multimodal alarm patterns, which are selectable to occur at different strengths. When a particular sensory modality of alerting is used to provide notifications of different event types, the signals may differ in amplitude (e.g., strength of signal), pattern (e.g., long or short bursts, inter burst-interval), or frequency (e.g., a 500 or 2000 Hz sound). It would be helpful to perform various back-up/compensatory operations if the internal and external alerting did not occur as expected and to be able to quantify and detect these operational deviations. Transducer malfunction can cause normally distinct types of notification to be mistaken, or ignored, by the patient.
US patent application 2009/0072768, entitled “Use of an accelerometer to control vibration performance” to Murray el al. teaches using an accelerometer to measure the performance of a vibration motor and to increase, in a closed loop manner, the voltage applied to the drive circuit to compensate for changes in the speed of rotation that may occur over time. U.S. Pat. No. 6,774,769 to Okada entitled “Vibrating Alert Device” describes a method of increasing the voltage applied to a vibration alarm so that it increases gently over time and does not startle a user of the device.